1. Field of the Invention
This invention relates in general to multiple library data storage systems, and more particularly to a multiple host data storage system for a multi-library system.
2. Description of Related Art
The implementation of new technology in magnetic tape and optical storage products has meant that the density of data written has increased by orders of magnitude in the last ten or fifteen years. The ability to record high density tapes or optical media, e.g., ten gigabytes or more on one physical volume, has led to reducing costs in physical tape hardware as well as in handling and management resources.
However, over the past five years, data set stacking products, i.e., software solutions to increase tape and optical storage system utilization, have evolved in response to the customer requirement for more efficient ways to manage the information stored thereon. Often a library system is provided in conjunction with a library manger. For example, a virtual tape server (VTS) having a tape library has been proposed to achieve increased capacity. In a VTS, the hardware is transparent to a host and a user. The VTS requires little external management except though the library management element of the tape library into which a VTS is integrated.
In a hierarchical storage systems, such as a VTS, intensively used and frequently accessed data is stored in fast but expensive memory. One example of a fast memory is a direct access storage device (DASD). In contrast, less frequently accessed data is stored in less expensive but slower memory. Examples of slower memory are tape drives and disk drive arrays. The goal of the hierarchy is to obtain moderately priced, high-capacity storage while maintaining high-speed access to the stored information.
In the VTS system, a host interface, a DASD, and a number of tape devices are provided. When the host writes a logical volume, or a file, to the VTS, the data is stored as a file on the DASD. Although the DASD provides quick access to this data, it will eventually reach full capacity and a backup or secondary storage system will be needed. An IBM 3590 tape cartridge is one example of a tape device that could be used as a backup or secondary storage system.
When the DASD fills to a predetermined threshold, the logical volume data for a selected logical volume, typically the oldest, is removed from the DASD to free space for more logical volumes. The selected DASD file is then appended onto a tape cartridge, or a physical volume, with the original left on the DASD for possible cache hits. When a DASD file has been appended to a tape cartridge and the original remains on the DASD, the file is "premigrated".
When the host reads a logical volume from the VTS, a cache hit occurs if the logical volume currently resides on the DASD. If the logical volume is not on the DASD, the storage manager determines which of the physical tape volumes contains the logical volume. The corresponding physical volume is then mounted on one of the tape devices, and the data for the logical volume is transferred back to the DASD from the tape.
Tape servers may use an engine to move data between the DASD and tape drives in a virtual tape server (VTS) environment. For example, the IBM Virtual Tape Server (VTS) uses the IBM Adstar Distributed Storage Manager (ADSM) as its engine to move data between the DASD and IBM 3590 tape drives on the VTS. In such a system, the VTS uses the storage manager client on the DASD, e.g., the ADSM Hierarchical Storage Manager (HSM) client, and a distributed storage manager server attached to the tape drives to provide this function.
A library dataserver provides automated storage for multiple applications such as mid-range computer facilities, LAN servers and archiving applications. To provide high frequency to data, high storage capacity and high performance must be combined. Therefore, knowing the location of data storage media in the library is paramount. Typically, the data storage media are bar-coded with a serial number or other identifying marking. Thus, an accessor that is equipped with a bar-code reader can access any cartridge in the library. In addition, the accessor can mount any cartridge located in the library on any library drive. The accessor's management feature permits rapid scanning of all cartridge bar-codes.
One function of a library dataserver is to provide an update of the locations of data storage media in that library upon resumption of automated operations after the library has been paused and had at least one door opened. Since, while paused, the operator can open any number of doors and move data storage media within the frames of these opened doors, a scan operation must occur to determine which, if any, data storage media have been added, removed, or moved within such frames. Since the location of data storage media within such a library are not known with certainty, any host requests to mount or demount data storage media are held until an inventory update procedure has completed. Once the library system inventory has been updated, data storage media may be accessed by a host.
However, to connect multiple hosts to a multi-library system, additional hardware, such as extra adapters and cables, is required. Still, there are several disadvantages to a multiple host system that is configured using multiple adapters and cabling. For example, data access is slowed due to the involvement of multiple adapters and the accompanying congestion.
It can be seen that there is a need for a method and apparatus that enables multiple host connections with a multi-library system without the traditional drawbacks.
It can also be seen that there is a need for a method and apparatus that allows dynamic tracking of all physical cartridge locations and provides continuous updates.
It can also be seen that there is a need for a method and apparatus that intercepts move or exchange commands from multiple hosts, converts them to the physical element address locations, and then executes the commands.